Fusion proteins for prodrug activation

ABSTRACT

The invention relates to compounds which contain an antigen binding region which is bound to at least one enzyme which is able to metabolize a compound (prodrug) which has little or no cytotoxicity to a cytotoxic compound (drug), where the antigen binding region is composed of a single polypeptide chain. It is advantageous for covalently bonded carbohydrates to be present on the polypeptide chain.

The invention relates to compounds which contain an antigen binding region which is bound to at least one enzyme which is able to metabolize a compound (prodrug) which has little or no cytotoxicity to a cytotoxic compound (drug), where the antigen binding region is composed of a single polypeptide chain. It is advantageous for covalently bonded carbohydrates to be present on the polypeptide chain.

The combination of prodrug and antibody-enzyme conjugates for use as therapeutic composition has already been described in the specialist literature. This entails antibodies which are directed against a particular tissue and to which a prodrug-cleaving enzyme is bound being injected into an organism, and subsequently a prodrug compound which can be activated by the enzyme being administered. The action of the antibody-enzyme conjugate bound to the target tissue is intended to convert the prodrug compound into a compound which exerts a cytotoxic effect on the bound tissue. However, studies on antibody-enzyme conjugates have shown that these chemical conjugates have unfavorable pharmacokinetics so that there is only inadequate site-specific tumor-selective cleavage of the prodrug. Some authors have attempted to remedy this evident deficiency by additional injection of an anti-enzyme antibody which is intended to bring about rapid elimination of the antibody-enzyme conjugate from the plasma (Sharma et al., Brit. J. Cancer, 61, 659, 1990). Another problem of antibody-enzyme conjugates is the limited possibility of preparing large amounts reproducibly and homogeneously.

The object of the present invention was now to find fusion proteins which can be prepared on an industrial scale and are suitable, by reason of their pharmacokinetic and pharmacodynamic properties, for therapeutic uses.

It has been found in this connection that compounds which contain an antigen binding region which is composed of a single polypeptide chain have unexpected advantages for the preparation and use of fusion proteins, to which carbohydrates are advantageously attached, in prodrug activation.

The invention therefore relates to compounds which contain an antigen binding region which is bound to at least one enzyme, where the antigen binding region is composed of a single polypeptide chain, and carbohydrates are advantageously attached to the fusion protein.

An antigen binding region means for the purpose of the invention a region which contains at least two variable domains of an antibody, preferably one variable domain of a heavy antibody chain and one variable domain of a light antibody chain (sFv fragment). The antigen binding region can, however, also have a bi- or multivalent structure, i.e. two or more binding regions, as described, for example, in EP-A-0 404 097. However, a human or humanized sFv fragment is particularly preferred, especially a humanized sFv fragment.

The antigen binding region preferably binds to a tumor-associated antigen (TAA), with the following TAAs being particularly preferred:

-   neural cell adhesion molecule (N-CAM), -   polymorphic epithelial mucin (PEM), -   epidermal growth factor receptor (EGF-R), -   Thomsen Friedenreich antigen β (TFβ), -   gastrointestinal tract carcinoma antigen (GICA), -   ganglioside GD_(3 (GD3)), -   ganglioside GD₂ (GD₂), -   Sialyl-Le^(a), Sialyl-Le^(x), -   TAG72, -   the 24-25 kDa glycoprotein defined by MAb L6, -   CA 125 and, especially, -   carcinoembryonic antigen (CEA).

Preferred enzymes are those enzymes which are able to metabolize a compound of little or no cytotoxicity to a cytotoxic compound. Examples are β-lactamase, pyroglutamate aminopeptidase, galactosidase or D-aminopeptidase as described, for example, in EP-A2-0 382 411 or EP-A2-0 392 745, an oxidase such as, for example, ethanol oxidase, galactose oxidase, D-amino-acid oxidase or α-glyceryl-phosphate oxidase as described, for example, in WO 91/00108, peroxidase as disclosed, for example, in EP-A2-0 361 908, a phosphatase as described, for example, in EP-Al-0 302 473, a hydroxynitrilelyase or glucosidase as disclosed, for example, in WO 91/11201, a carboxypeptidase such as, for example, carboxypeptidase G2 (WO 88/07378), an amidase such as, for example, penicillin 5-amidase (Kerr, D. E. et al. Cancer Immunol. Immunther. 1990, 31) and a protease, esterase or glycosidase such as the already mentioned galactosidase, glucosidase or a glucuronidase as described, for example, in WO 91/08770.

A β-glucuronidase is preferred, preferably from Kobayasia nipponica or Secale cereale, and more preferably from E. coli or a human β-glucuronidase. The substrates for the individual enzymes are also indicated in the said patents and are intended also to form part of the disclosure content of the present application. Preferred substrates of βglucuronidase are N-(D-glyco-pyranosyl)benzyloxycarbonylanthracyclines and, in particular, N-(4-hydroxy3-nitrobenzyloxycarbonyl)doxorubicin and daunorubicin β-D-glucuronide (J. C. Florent et al. (1992) Int. Carbohydr. Symp. Paris, A262, 297 or S. Andrianomenjanahary et al. (1992) Int. Carbohydr. Symp. Paris, A 264, 299).

The invention further relates to nucleic acids which code for the compounds according to the invention. Particularly preferred is a nucleic acid, as well as its variants and mutants, which codes for a humanized sFv fragment against CEA (carcinoembryonic antigen) linked to a human β-glucuronidase, preferably with the sequence indicated in Table 1 (sFv-huβ-Gluc).

The compounds according to the invention are prepared in general by methods of genetic manipulation which are generally known to the skilled worker, it being possible for the antigen binding region to be linked to one or more enzymes either directly or via a linker, preferably a peptide linker. The peptide linker which can be used is, for example, a hinge region of an antibody or a hinge-like amino-acid sequence. In this case, the enzyme is preferably linked with the N terminus to the antigen binding region directly or via a peptide linker. The enzyme or enzymes can, however, also be linked to the antigen binding region chemically as described, for example, in WO 91/00108.

The nucleic acid coding for the amino-acid sequence of the compounds according to the invention is generally cloned in an expression vector, introduced into prokaryotic or eukaryotic host cells such as, for example, BHK, CHO, COS, HeLa, insect, tobacco plant, yeast or E. coli cells and expressed. The compound prepared in this way can subsequently be isolated and used as diagnostic aid or therapeutic agent. Another generally known method for the preparation of the compound according to the invention is the expression of the nucleic acids which code therefor in transgenic mammals with the exception of humans, preferably in a transgenic goat.

BHK cells transfected with the nucleic acids according to the invention express a fusion protein (sFv-huβ-Gluc) which not only was specific for CEA but also had full β-glucuronidase activity (see Example 5).

This fusion protein was purified by anti-idiotype affinity chromatography in accordance with the method described in EP 0 501 215 A2 (Example M). The fusion protein purified in this way gives a molecular weight of 100 kDA in the SDS PAGE under reducing conditions, while molecules of 100 and 200 kDa respectively appear under non-reducing conditions.

Gel chromatography under native conditions (TSK-3000 gel chromatography) showed one protein peak (Example 6, FIG. I) which correlates with the activity peak in the specificity enzyme activity test (EP 0 501 215 A2). The position of the peak by comparison with standard molecular weight markers indicates a molecular weight of ≈200 kDa. This finding, together with the data from the SDS PAGE, suggests that the functional enzymatically active sFv-huβ-Gluc fusion protein is in the form of a “bivalent molecule”, i.e. with 2 binding regions and 2 enzyme molecules. Experiments not described here indicate that the fusion protein may, under certain cultivation conditions, be in the form of a tetramer with 4 binding regions and 4 enzyme molecules. After the sFv-huβ-Gluc fusion protein had been purified and undergone functional characterization in vitro, the-pharmacokinetics and the tumor localization of the fusion protein were determined in nude mice provided with human gastric carcinomas. The amounts of functionally active fusion protein were determined in the organs and in the tumor at various times after appropriate workup of the organs (Example 7) and by immunological determination (triple determinant test, Example 8). The results of a representative experiment are compiled in Table 4.

Astonishingly, a tumor/plasma ratio of 5/1 is reached after only 48 hours. At later times, this ratio becomes even more favorable and reaches values >200/1 (day 5). The reason for this favorable pharmacokinetic behavior of the sFv-huβ-Gluc fusion protein is that fusion protein not bound to the tumor is removed from the plasma and the normal tissues by internalization mainly by receptors for mannose 6-phosphate and galactose. (Evidence for this statement is that there is an intracellular increase in the β-glucuronidase level, for example in the liver).

As shown in Table 5, the sFv-huβ-Gluc contains relatively large amounts of galactose and, especially, mannose, which are mainly responsible for the binding to the particular receptors. The fusion protein/receptor complex which results and in which there is binding via the carbohydrate residues of the fusion protein is then removed from the extracellular compartment by internalization.

This rapid internalization mechanism, which is mainly mediated by galactose and mannose, is closely involved in the advantageous pharmacokinetics of the fusion protein according to the invention. These advantageous pharmacokinetics of the fusion protein to which galactose and, in particular, mannose are attached makes it possible for a hydrophilic prodrug which undergoes extracellular distribution to be administered i.v. at a relatively early time without eliciting non-specific prodrug activation. In this case an elimination step as described by Sharma et al. (Brit. J. Cancer, 61, 659, 1990) is unnecessary. Based on the data in Table 4, injection of a suitable prodrug (S. Adrianomenjanahari et al. 1992, Int. Carbohydrate Symp., Parts A264, 299) is possible even 3 days after injection of the sFv-huβ-Gluc fusion protein without producing significant side effects (data not shown).

A similarly advantageous attachment of carbohydrates to fusion proteins can also be achieved, for example, by secretory expression of the sFv-huβ-Gluc fusion protein in particular yeast strains such as Saccharomyces cerevisiae or Hansenula polymorpha. These organisms are capable of very effective mannosylation of fusion proteins which have appropriate N-glycosylation sites (Goochee et al., Biotechnology, 9, 1347-1354, 1991). Such fusion proteins which have undergone secretory expression in yeast cells show a high degree of mannosylation and favorable pharmacokinetics comparable to those of the sFv-huβ-Gluc fusion protein expressed in BHK cells (data not shown). In this case, the absence of galactose is compensated by the even higher degree of mannosylation of the fusion protein (Table 6). The sFv-huβ-Gluc fusion protein described above was constructed by genetic manipulation and expressed in yeast as described in detail in Example 9.

Instead of human β-glucuronidase it is, however, also possible to employ another glucuronidase with advantageous properties. For example, the E. coli β-glucuronidase has the particular advantage that its catalytic activity at pH 7.4 is significantly higher than that of human β-glucuronidase. In Example 10, an sFv-E. coli β-Gluc construct was prepared by methods of genetic manipulation and underwent secretory expression as functionally active mannosylated fusion protein in Saccharomyces cerevisiae. The pharmacokinetic data are comparable to those of the sFv-huβ-Gluc molecule which was expressed in yeast or in BHK cells (Table 4).

The glucuronidases from the fungus Kobayasia nipponica and from the plants Secale cereale have the advantage, for example, that they are also active as monomers. In Example 11, methods of genetic manipulation were used to prepare a construct which, after expression in Saccharomyces cerevisiae, excretes an sFv-B. cereus β-lactamase II fusion protein preferentially in mannosylated form.

This fusion protein likewise has, as the fusion proteins according to the invention, on the basis of β-glucuronidase pharmacokinetics which are favorable for prodrug activation (Table 4).

Furthermore, the compounds according to the invention can be employed not only in combination with a prodrug but also in the framework of conventional chemotherapy in which cytostatics which are metabolized as glucuronides and thus inactivated can be converted back into their toxic form by the administered compounds.

The following examples now describe the synthesis by genetic manipulation of sFv-β-Gluc fusion proteins, and the demonstration of the ability to function.

The starting material comprised the plasmids pABstop 431/26 hum V_(H) and pABstop 431/26 hum VH_(L). These plasmids contain the humanized version of the V_(H) gene and V_(L) gene of anti-CEA MAb BW 431/26 (Gussow and Seemann, 1991, Meth. Enzymology, 203, 99-121). Further starting material comprised the plasmid pABstop 431/26 V_(H)-huβ-Gluc 1H (EP-A2-0 501 215) which contains a V_(H) exon, including the V_(H)-intrinsic signal sequence, followed by a CHl exon, by the hinge exon of a human IgG3 C gene and the complete cDNA of human β-glucuronidase.

EXAMPLE 1

Amplification of the V_(H) and V_(L) Genes of MAb hum 431/26

The oligonucleotides pAB-Back and linker-anti (Tab. 2) are used to amplify the V_(H) gene including the signal sequence intrinsic to the V_(H) gene from pABstop 431V_(H) hum (V_(H) 431/26) (Gussow and Seemann, 1991, Meth. Enzymology, 203, 99-121). The oligonucleotides linker-sense and V_(L(Mut))-For (Tab. 3) are used to amplify the V_(L) gene from pABstop 431V_(L) hum (V_(L) 431/26).

EXAMPLE 2

Joining of the V_(H) 431/26 and V_(L) 431/26 Gene Fragments

The oligonucleotides linker-anti and linker-sense are partially complementary with one another and encode a polypeptide linker which is intended to link the V_(H) domain and V_(L) domain to give an sFv fragment. In order to fuse the amplified V_(H) fragments with the V_(L) fragments, they are purified and employed in a 10-cycle reaction as follows: H₂O: 37.5 μl dNTPs (2.5 mM): 5.0 μl PCR buffer (10×): 5.0 μl Taq polymerase (Perkin-Elmer Corp., Emmeryville, CA) (2.5 U/μl): 0.5 μl 0.5 μg/μl DNA of the V_(L) frag.: 1.0 μl 0.5 μg/μl DNA of the V_(H) frag.: 1.0 μl PCR buffer (10×): 100 mM tris, pH 8.3, 500 mM KCl, 15 mM MgCl2, 0.1% (w/v) gelatin.

The surface of the reaction mixture is sealed with paraffin, and subsequently the 10-cycle reaction is carried out in a PCR apparatus programmed for 94° C., 1 min; 55° C., 1 min; 72° C., 2 min. 2.5 pmol of the flanking primer pAB-Back and V_(L(Mut))-For are added, and a further 20 cycles are carried out. The resulting PCR fragment is composed of the V_(H) gene which is linked to the V_(L) gene via a linker. The signal sequence intrinsic to the V_(H) gene is also present in front of the V_(H) gene.

The oligonucleotide V_(L(Mut))-For also results in the last nucleotide base of the V_(L) gene, a C, being replaced by a G. This PCR fragment codes for a humanized single-chain Fv (SFV 431/26).

EXAMPLE 3

Cloning of the sFv 431/26 Fragment into the Expression Vector which Contains the huβ-glucuronidase gene.

The sFv fragment from (2) is cut with HindIII and BamHI and ligated into the vector pAB 431V_(H) hum/CHl+1 h/β-Glc which has been completely cleaved with HindIII and partially cleaved with BglII. The vector pABstop 431/26V_(H)huβ-Gluc1H contains a V_(H) exon, including the V_(H)-intrinsic signal sequence, followed by a CHl exon, by the hinge exon of a human IgG3 C gene and by the complete cDNA of human β-glucuronidase. The plasmid clone pMCG-E1 which contains the humanized sFv 431/26, a hinge exon and the gene for human β-glucuronidase is isolated (pMCG-E1).

EXAMPLE 4

Expression of the sFv-hup-Gluc Fusion Protein in BEK Cells.

The clone pMCG-E1 is transfected with the plasmid pRMH 140 which harbors a neomycin-resistance gene and with the plasmid pSV2 which harbors a methotrexateresistance gene into BHK cells. The BHK cells subsequently express a fusion protein which has both the antigen-binding properties of MAb BW 431/26hum and the enzymatic activity of human β-glucuronidase.

EXAMPLE 5

Demonstration of the antigen-binding Properties and of the Enzymatic Activity of the sFv-huβ-Gluc Fusion Protein.

The ability of the sFv-huβ-Gluc fusion protein to bind specifically to the CEA epitope defined by 431/26 and simultaneously to exert the enzymatic activity of human β-glucuronidase was shown in a specificity enzyme activity test (EP-A2-0 501 215). The test determines the liberation of 4-methylumbelliferone from 4-methylumbelliferyl β-glucuronide by the β-glucuronidase portion of the fusion protein after the fusion protein has been bound via the sFv portion to an antigen. The measured fluorescence values are reported as relative fluorescence units (FU). The test shows a significant liberation of methyl-umbelliferone by the fusion protein in the plates coated with CEA. By contrast, the fusion protein does not liberate any methylumbelliferone in control plates coated with PEM (polymorphic epithelial mucin).

EXAMPLE 6

TSK 3000 Gel Chromatography

200 ng of the sFv-huβ-Gluc fusion protein which had been purified by anti-idiotype affinity chromatography in 25 μl were chromatographed on a TSK gel G 3000 SW XL column (TOSO HAAS Order No. 3.5Wx.N3211, 7.8 mm×300 mm) in a suitable mobile phase (PBS, pH 7.2, containing 5 g/l maltose and 4.2 g/l arginine) at a flow rate of 0.5 ml/ min. The Merck Hitachi HPLC system (L-4000 UV detector, L-6210 intelligent pump, D-2500 Chromato-integrator) was operated under ≈20 bar, the optical density of the eluate was determined at 280 nm, and an LKB 2111 Multisac fraction collector was used to collect 0.5 ml fractions which were subsequently analysed in a specificity enzyme activity test (SEAT) (EP 0 501 215 A2, Example J). The result of this experiment is shown in FIG. 1. It is clearly evident that the position of the peak detectable by measurement of the optical density at 280 nm coincides with the peak which determines the specificity and enzyme activity (SEAT) of the eluate. Based on the positions of the molecular weights of standard proteins which are indicated by arrows, it can be concluded that the functionally active sFv-huβ-Gluc fusion protein has an approximate molecular weight of ≈200 kDa under native conditions.

EXAMPLE 7

Workup of Organs/Tumors for Determination of the Fusion Protein

The following sequential steps were carried out:

-   -   nude mice (CDl) which have a subcutaneous tumor and have been         treated with fusion protein or antibody-enzyme conjugate undergo         retroorbital exsanguination and are then sacrificed     -   the blood is immediately placed in an Eppendorf tube which         already contains 10 μl of Liquemin 25000 (from Hoffman-LaRoche         AG)     -   centrifugation is then carried out in a centrifuge (Megafuge         1.0, from Heraeus) at 2500 rpm for 10 min     -   the plasma is then obtained and frozen until tested     -   the organs or the tumor are removed and weighed     -   they are then completely homogenized with 2 ml of 1% BSA in PBS,         pH 7.2     -   the tumor homogenates are adjusted to pH 4.2 with 0.1 N HCl (the         sample must not be overtitrated because β-glucuronidase is         inactivated at pH<3.8)     -   all the homogenates are centrifuged at 16000 g for 30 min     -   the clear supernatant is removed     -   the tumor supernatants are neutralized with 0.1 N NaOH     -   the supernatants and the plasma can now be quantified in         immunological tests.

EXAMPLE 8

Triple Determinant Test

The tests are carried out as follows:

-   -   75 μl of a mouse anti-huβ-Gluc antibody (MAb 2118/157         Behringwerke) diluted to 2 μg/ml in PBS, pH 7.2, are placed in         each well of a microtiter plate (polystyrene U-shape, type B,         from Nunc, Order No. 4-60445)     -   the microtiter plates are covered and incubated at R.T.         overnight     -   the microtiter plates are subsequently washed 3× with 250 μl of         0.05 M tris-citrate buffer, pH 7.4, per well     -   these microtiter plates coated in this way are incubated with         250 μl of blocking solution (1% casein in PBS, pH 7.2) in each         well at R.T. for 30′ (blocking of non-specific binding sites)         (coated microtiter plates which are not required are dried at         R.T. for 24 hours and then sealed together with drying         cartridges in coated aluminum bags for long-term storage)     -   during the blocking, in an untreated 96-well U-shaped microtiter         plate (polystyrene, from Renner, Order No. 12058), 10 samples+2         positive controls+1 negative control are diluted 1:2 in 1%         casein in PBS, pH 7.2, in 8 stages (starting from 150 μl of         sample, 75 μl of sample are pipetted into 75 μl of casein         solution etc.)     -   the blocking solution is aspirated out of the microtiter plate         coated with anti-huμ-Gluc antibodies, and 50 μl of the diluted         samples are transferred per well from the dilution plate to the         test plate and incubated at R.T. for 30 min     -   during the sample incubation, the ABC-AP reagent (from         Vectastain, Order No. AK-5000) is made up: thoroughly mix 2         drops of reagent A (Avidin DH) in 10 ml of 1% casein in PBS, pH         7.2, add 2 drops of reagent B (biotinylated alkaline         phosphatase) add mix thoroughly. (The ABC-AP solution must be         made up at least 30′ before use.)     -   the test plate is washed 3 times with ELISA washing buffer         (Behringwerke, Order No. OSEW 96)     -   50 μl of biotin-labeled detecting antibody mixture (1+1 mixture         of mouse anti 431/26 antibody (MAb 2064/353, Behringwerke) and         mouse anti-CEA antibody (MAb 250/183, Behringwerke) in a         concentration of 5 μg/ml diluted in 1% casein in PBS, pH 7.2,         final concentration of each antibody of 2.5 μg/ml) are placed in         each well     -   the test plate is washed 3 times with ELISA washing buffer     -   50 μl of the prepared ABC-AP solution are placed in each well         and incubated at R.T. for 30 min     -   during the ABC-AP incubation, the substrate is made up (fresh         substrate for each test: 1 mM 4-methylum-belliferyl phosphate,         Order No. M-8883, from Sigma, in 0.5 M tris+0.01% MgCl₁ pH 9.6)     -   the test plate is washed 7 times with ELISA washing buffer     -   50 μl of substrate are loaded into each well, and the test plate         is covered and incubated at 37° C. for 2 h     -   150 μl of stop solution (0.2 M glycine+0.2% SDS, pH 11.7) are         subsequently added to each well     -   the fluorometric evaluation is carried out in a Fluoroscan II         (ICN Biomedicals, Cat. No. 78-611-00) with an excitation         wavelength of 355 nm and an emission wavelength of 460 nm     -   the unknown concentration of fusion protein in the sample is         determined on the basis of the fluorescence values for the         positive control included in the identical experiment (dilution         series with purified sFv-huβ-Gluc mixed with CEA 5 μg/ml as         calibration plot).

EXAMPLE 9

Expression of the sPv-huβ-Gluc Fusion Protein in Yeast.

The single-chain Fv (sFv) from Example 2 is amplified with the oligos 2577 and 2561 (Table 7) and cloned into the vector pUC19 which has been digested with XbaI/HindIII (FIG. 2).

The human β-glucuronidase gene is amplified with the oligos 2562 and 2540 (Table 8) from the plasmid pAB 431/26 V_(H)hum/CHl+1H/β-Gluc (Example 3) and ligated into the plasmid sFv 431/26 in pUC19 (FIG. 2) cut with BglII/HindIII (FIG. 3).

A KpnI/NcoI fragment is amplified with the oligos 2587 and 2627 (Table 9) from the sFv 431/26 and cloned into the yeast expression vector pIXY digested with KpnI/NcoI (FIG. 4).

The BstEII/HindIII fragment from the plasmid sFv 431/26 huβ-Gluc in pUC19 (FIG. 3) is ligated into the vector pIXY 120 which harbors the V_(H) gene, the linker and a part of the V_(L) gene (V_(H)/link/V_(K) part. in pIXY 120) and has been digested with BstEII/partially with HindIII (FIG. 5).

The resulting plasmid sFv 431/26 huβ-Gluc in PIXY 120 is transformed into Saccharomyces cerevisiae and the fusion protein is expressed.

EXAMPLE 10

Expression of the sFv-E. coli-β-glucuronidase Fusion Protein in Yeast.

The E. coli glucuronidase gene is amplified from PRAJ 275 (Jefferson et al. Proc. Natl. Acad. Sci, USA, 83: 8447-8451, 1986) with the oligos 2638 and 2639 (Table 10) and ligated into sFv 431/26 in pUC19 (Example 9, FIG. 2) cut with BglII/HindIII (FIG. 6).

A BstEII/HindIII fragment from sFv 431/26 E. coli β-Gluc in pUC19 is cloned into the vector V_(H)/link/V_(K) part in pIXY 120 (Example 9, FIG. 4) which has been partially digested with BstEII/HindIII (FIG. 7).

The plasmid sFv 431/26 E. coli β-Gluc in PIXY 120 is transformed into Saccharomyces cerevisiae and the fusion protein is expressed.

EXAMPLE 11

Expression of the sFv-β-lactamase Fusion Protein in Yeast.

The single-chain Fv (sFv) from Example 2 is amplified with the oligos 2587 and 2669 (Table 11) and ligated into the pUC19 vector digested with KpnI/HindIII (FIG. 8).

The β-lactamase II gene (Hussain et al., J. Bacteriol. 164: 223-229, 1985) is amplified with the oligos 2673 and 2674 (Table 11) from the complete DNA of Bacillus cereus and ligated into the pUC19 vector digested with EcoRI/HindIII (FIG. 9). A BclI/HindIII fragment of the β-lactamase gene is ligated into sFv 431/26 in pUC19 which has been cut with BglII/HindIII (FIG. 10).

The KpnI/HindIII sFv-β-lactamase fragment is ligated into pIXY 120 which has been digested with KpnI/partially with HindIII (FIG. 11). The plasmid is transformed into Saccharomyces cerevisiae, and a fusion protein which has both the antigen-binding properties of MAb 431/26 and the enzymatic activity of Bacillus cereus β-lactamase is expressed. TABLE 1 CCAAGCTTAT GAATATGCAA ATCCTGCTCA TGAATATGCA AATCCTCTGA 50 ATCTACATGG TAAATATAGG TTTGTCTATA CCACAAACAG AAAAACATGA 100 GATCACAGTT CTCTCTACAG TTACTGAGCA CACAGGACCT CACC ATG GGA TGG 153                                                  Met Gly Trp AGC TGT ATC ATC CTC TTC TTG GTA GCA ACA GCT ACA GGTAAGGGGC 199 Ser Cys Ile Ile Leu Phe Leu Val Ala Thr Ala Thr                         −10 TCACAGTAGC AGGCTTGAGG TCTGGACATA TATATGGGTG ACAATGACAT 249 CCACTTTGCC TTTCTCTCCA CA GGT GTC CAC TCC CAG GTC CAA CTG CAG 298                          Gly Val His Ser Gln Val Gln Leu Gln                                          1 GAG AGC GGT CCA GGT CTT GTG AGA CCT AGC CAG ACC CTG AGC CTG 343 Glu Ser Gly Pro Gly Leu Val Arg Pro Ser Gln Thr Leu Ser Leu                  10                                      20 ACC TGC ACC GTG TCT GGC TTC ACC ATC AGC AGT GGT TAT AGC TGG 388 Thr Cys Thr Val Ser Gly Phe Thr Ile Ser Ser Gly Tyr Ser Trp                                      30 CAC TGG GTG AGA CAG CCA CCT GGA CGA GGT CTT GAG TGG ATT GGA 433 His Trp Val Arg Gln Pro Pro Gly Arg Gly Leu Glu Trp Ile Gly                  40                                      50 TAC ATA CAG TAC AGT GGT ATC ACT AAC TAC AAC CCC TCT CTC AAA 478 Tyr Ile Gln Tyr Ser Gly Ile Thr Asn Tyr Asn Pro Ser Leu Lys                                      60 AGT AGA GTG ACA ATG CTG GTA GAC ACC AGC AAG AAC CAG TTC AGC 523 Ser Arg Val Thr Met Leu Val Asp Thr Ser Lys Asn Gln Phe Ser                  70                                      80 CTG ACA CTC AGC ACC GTG ACA GCC GCC GAC ACC GCG GTC TAT TAT 568 Leu Arg Leu Ser Ser Val Thr Ala Ala Asp Thr Ala Val Tyr Tyr                                      90 TGT GCA AGA GAA GAC TAT GAT TAC CAC TGG TAC TTC GAT GTC TGG 613 Cys Ala Arg Glu Asp Tyr Asp Tyr His Trp Tyr Phe Asp Val Trp                 100                                     110 GGC CAA GGG ACC ACG GTC ACC GTC TCC TCA GGA GGC GGT GGA TCG 658 Gly Gln Gly Thr Thr Val Thr Val Ser Ser Gly Gly Gly Gly Ser                                     120 GGC GGT GGT GGG TCG GGT GGC GGC GGA TCT GAC ATC CAG CTG ACC 703 Gly Gly Gly Gly Ser Gly Gly Gly Gly Ser Asp Ile Gln Leu Thr                 130                                     140 CAG AGC CCA AGC AGC CTG AGC GCC AGC GTG GGT GAC AGA GTG ACC 748 Gln Ser Pro Ser Ser Leu Ser Ala Ser Val Gly Asp Arg Val Thr                                     150 ATC ACC TGT AGT ACC AGC TCG AGT GTA AGT TAC ATG CAC TGG TAC 793 Ile Thr Cys Ser Thr Ser Ser Ser Val Ser Tyr Met His Trp Tyr                 160                                     170 CAG CAG AAG CCA GGT AAG GCT CCA AAG CTG CTG ATC TAC AGC ACA 838 Gln Gln Lys Pro Gly Lys Ala Pro Lys Leu Leu Ile Tyr Ser Thr                                     180 TCC AAC CTG GCT TCT GGT GTG CCA AGC AGA TTC AGC GGT AGC GGT 883 Ser Asn Leu Ala Ser Gly Val Pro Ser Arg Phe Ser Gly Ser Gly                 190                                     200 AGC GGT ACC GAC TTC ACC TTC ACC ATC AGC AGC CTC CAG CCA GAG 928 Ser Gly Thr Asp Phe Thr Phe Thr Ile Ser Ser Leu Gln Pro Glu                                     210 GAC ATC GCC ACC TAC TAC TGC CAT CAG TGG AGT AGT TAT CCC ACG 973 Asp Ile Ala Thr Tyr Tyr Cys His Gln Trp Ser Ser Tyr Pro Thr                     220                                 230 TTC GGC CAA GGG ACC AAG CTG GAG ATC AAA GGTGAGTAGA ATTTAAACTT 1023 Phe Gly Gln Gly Thr Lys Leu Glu Ile Lys                                     240 TGCTTCCTCA GTTGGATCTG AGTAACTCCC AATCTTCTCT CTGCA GAG CTC AAA 1077                                                   Glu Leu Lys ACC CCA CTT GGT GAC ACA ACT CAC ACA TGC CCA CGG TGC CCA 1119 Thr Pro Leu Gly Asp Thr Thr His Thr Cys Pro Arg Cys Pro                         250 GGTAAGCCAG CCCAGGACTC GCCCTCCAGC TCAAGGCGGG ACAAGAGCCC 1169 TAGAGTGGCC TGAGTCCAGG GACAGGCCCC AGCAGGGTGC TGACGCATCC 1219 ACCTCCATCC CAGATCCCCG TAACTCCCAA TCTTCTCTCT GCA GCG GCG GCG 1271                                                 Ala Ala Ala                                                         260 GCG GTG CAG GGC GGG ATG CTG TAC CCC CAG GAG AGC CCG TCG CGG 1316 Ala Val Gln Gly Gly Met Leu Tyr Pro Gln Glu Ser Pro Ser Arg                                     270 GAG TGC AAG GAG CTG GAC GGC CTC TGG AGC TTC CGC GCC GAC TTC 1361 Glu Cys Lys Glu Leu Asp Gly Leu Trp Ser Phe Arg Ala Asp Phe                 280                                     290 TCT GAC AAC CGA CGC CGG GGC TTC GAG GAG CAG TGG TAC CGG CGG 1406 Ser Asp Asn Arg Arg Arg Gly Phe Glu Glu Gln Trp Tyr Arg Arg                                     300 CCG CTG TGG GAG TCA GGC CCC ACC GTG GAC ATG CCA GTT CCC TCC 1451 Pro Leu Trp Glu Ser Gly Pro Thr Val Asp Met Pro Val Pro Ser                 310                                     320 AGC TTC AAT GAC ATC AGC CAG GAC TGG CGT CTG CGG CAT TTT GTC 1496 Ser Phe Asn Asp Ile Ser Gln Asp Trp Arg Leu Arg His Phe Val                                     330 GGC TGG GTG TGG TAC GAA CGG GAG GTG ATC CTG CCG GAG CGA TGG 1541 Gly Trp Val Trp Tyr Glu Arg Glu Val Ile Leu Pro Glu Arg Trp                 340                                     350 ACC CAG GAC CTG CGC ACA AGA GTG GTG CTG AGG ATT GGC AGT GCC 1586 Thr Gln Asp Leu Arg Thr Arg Val Val Leu Arg Ile Gly Ser Ala                                     360 CAT TCC TAT CCC ATC GTG TGG GTG AAT GGG GTC GAC ACG CTA GAG 1631 His Ser Tyr Ala Ile Val Trp Val Asn Gly Val Asp Thr Leu Glu                 370                                     380 CAT GAG GGG CCC TAC CTC CCC TTC GAG GCC GAC ATC AGC AAC CTG 1676 His Glu Gly Gly Tyr Leu Pro Phe Glu Ala Asp Ile Ser Asn Leu                                     390 GTC CAG GTG GGG CCC CTG CCC TCC CGG CTC CGA ATC ACT ATC GCC 1721 Val Gln Val Gly Pro Leu Pro Ser Arg Leu Arg Ile Thr Ile Ala                 400                                     410 ATC AAC AAC ACA CTC ACC CCC ACC ACC CTG CCA CCA GGG ACC ATC 1766 Ile Asn Asn Thr Leu Thr Pro Thr Thr Leu Pro Pro Gly Thr Ile                                     420 CAA TAC CTG ACT GAC ACC TCC AAG TAT CCC AAG GGT TAC TTT GTC 1811 Gln Tyr Leu Thr Asp Thr Ser Lys Tyr Pro Lys Gly Tyr Phe Val                 430                                     440 CAG AAC ACA TAT TTT GAC TTT TTC AAC TAC GCT GGA CTG CAG CGG 1856 Gln Asn Thr Tyr Phe Asp Phe Phe Asn Tyr Ala Gly Leu Gln Arg                                     450 TCT GTA CTT CTG TAC ACG ACA CCC ACC ACC TAC ATC GAT GAC ATC 1901 Ser Val Leu Leu Tyr Thr Thr Pro Thr Thr Tyr Ile Asp Asp Ile                 460                                     470 ACC GTC ACC ACC AGC GTG GAG CAA GAC AGT GGG CTG GTG AAT TAC 1946 Thr Val Thr Thr Ser Val Glu Gln Asp Ser Gly Leu Val Asn Tyr                                     480 CAG ATC TCT GTC AAG GGC AGT AAC CTG TTC AAG TTG GAA GTG CGT 1991 Gln Ile Ser Val Lys Gly Ser Asn Leu Phe Lys Leu Glu Val Arg                 490                                     500 CTT TTG GAT GCA GAA AAC AAA GTC GTG CCC AAT GGG ACT GGG ACC 2036 Leu Leu Asp Ala Glu Asn Lys Val Val Ala Asn Gly Thr Gly Thr                                     510 CAG GCC CAA CTT AAC GTG CCA GGT GTC ACC CTC TGG TGG CCC TAC 2081 Gln Gly Gln Leu Lys Val Pro Gly Val Ser Leu Trp Trp Pro Tyr                 520                                     530 CTG ATG CAC GAA CGC CCT GCC TAT CTG TAT TCA TTG GAG GTG CAG 2126 Leu Met His Glu Arg Pro Ala Tyr Leu Tyr Ser Leu Glu Val Gln                                     540 CTG ACT GCA CAG ACG TCA CTG GGG CCT GTG TCT CAC TTC TAC ACA 2171 Leu Thr Ala Gln Thr Ser Leu Gly Pro Val Ser Asp Phe Tyr Thr                 550                                     560 CTC CCT GTG CCC ATC CGC ACT GTG GCT GTC ACC AAG AGC CAG TTC 2216 Leu Pro Val Gly Ile Arg Thr Val Ala Val Thr Lys Ser Gln Phe                                     570 CTC ATC AAT GGG AAA CCT TTC TAT TTC CAC GGT GTC AAC AAG CAT 2261 Leu Ile Asn Gly Lys Pro Phe Tyr Phe His Gly Val Asn Lys His                 580                                     590 GAG GAT GCG GAC ATC CGA GGG AAG GCC TTC GAC TCG CCC CTG CTG 2306 Glu Asp Ala Asp Ile Arg Gly Lys Gly Phe Asp Trp Pro Leu Leu                                     600 CTG AAG GAC TTC AAC CTG CTT CGC TGG CTT GGT GCC AAC GCT TTC 2351 Val Lys Asp Phe Asn Leu Leu Arg Trp Leu Gly Ala Asn Ala Phe                 610                                     620 CGT ACC AGC CAC TAC CCC TAT GCA GAG CAA GTC ATG CAC ATG TGT 2396 Arg Thr Ser His Tyr Pro Tyr Ala Glu Glu Val Met Gln Met Cys                                     630 GAC CCC TAT GCG ATT GTG GTC ATC GAT GAG TGT CCC GGC CTG CCC 2441 Asp Arg Tyr Gly Ile Val Val Ile Asp Glu Cys Pro Gly Val Gly                 640                                     650 CTG GCG CTC CCG CAG TTC TTC AAC AAC GTT TCT CTG CAT CAC CAC 2486 Leu Ala Leu Pro Gln Phe Phe Asn Asn Val Ser Leu His His His                                     660 ATG CAC CTG ATC GAA CAA GTG GTG CGT AGC GAC AAG AAC CAC CCC 2531 Met Gln Val Met Glu Glu Val Val Arg Arg Asp Lys Asn His Pro                 670                                     680 GCG GTC GTG ATG TGG TCT GTG GCC AAC GAG CCT GCG TCC CAC CTA 2576 Ala Val Val Met Trp Ser Val Ala Asn Glu Pro Ala Ser His Leu                                     690 GAA TCT GCT GGC TAC TAC TTG AAG ATG GTG ATC GCT CAC ACC AAA 2621 Glu Ser Ala Gly Tyr Tyr Leu Lys Met Val Ile Ala His Thr Lys                 700                                     710 TCC TTG GAC CCC TCC CGG CCT GTG ACC TTT GTG AGC AAC TCT AAC 2666 Ser Leu Asp Pro Ser Arg Pro Val Thr Phe Val Ser Asn Ser Asn                                     720 TAT GCA GCA GAC AAG GGG GCT CCG TAT GTG GAT GTG ATC TGT TTG 2711 Tyr Ala Ala Asp Lys Gly Ala Pro Tyr Val Asp Val Ile Cys Leu                 730                                     740 AAC AGC TAC TAC TCT TGG TAT CAC GAC TAC GGG CAC CTG GAG TTG 2756 Asn Ser Tyr Tyr Ser Trp Tyr His Asp Tyr Gly His Leu Glu Leu                                     750 ATT CAG CTG CAG CTG GCC ACC CAG TTT GAG AAC TGG TAT AAG AAG 2801 Ile Gln Leu Gln Leu Ala Thr Gln Phe Glu Asn Trp Tyr Lys Lys                 760                                     770 TAT CAG AAG CCC ATT ATT CAG AGC GAG TAT GGA GCA GAA ACG ATT 2846 Tyr Gln Lys Pro Ile Ile Gln Ser Glu Tyr Gly Ala Glu Thr Ile                                     780 GCA GGG TTT CAC CAG GAT CCA CCT CTG ATG TTC ACT GAA GAG TAC 2891 Ala Gly Phe His Gln Asp Pro Pro Leu Met Phe Thr Glu Glu Tyr                 790                                     800 CAG AAA AGT CTG CTA GAG CAG TAC CAT CTG GGT CTG GAT CAA AAA 2936 Gln Lys Ser Leu Leu Glu Gln Tyr His Leu Gly Leu Asp Gln Lys                                     810 CGC AGA AAA TAT GTG GTT GGA GAG CTC ATT TGG AAT TTT GCC GAT 2981 Arg Arg Lys Tyr Val Val Gly Glu Leu Ile Trp Asn Phe Ala Asp                     820                                 830 TTC ATG ACT GAA CAG TCA CCG ACG AGA GTG CTG GGG ATT AAA AAG 3026 Phe Met Thr Glu Gln Ser Pro Thr Arg Val Leu Gly Asn Lys Lys                                     840 GGG ATC TTC ACT CGG CAG AGA CAA CCA AAA AGT GCA GCG TTC CTT 3071 Gly Ile Phe Thr Arg Gln Arg Gln Pro Lys Ser Ala Ala Phe Leu                 850                                     860 TTG CGA GAG AGA TAC TGG AAG ATT GCC AAT GAA ACC AGG TAT CCC 3116 Leu Arg Glu Arg Tyr Trp Lys Ile Ala Asn Glu Thr Arg Tyr Pro                                     870 CAC TCA GTA GCC AAG TCA CAA TGT TTG GAA AAC AGC CCG TTT ACT 3161 His Ser Val Ala Lys Ser Gln Cys Leu Glu Asn Ser Pro Phe Thr                 880                                     890 TGA GCAAGACTGA TACCACCTGC GTGTCCCTTC CTCCCCGAGT CAGGGCGACT 3214 ... TCCACAGCAG CAGAACAAGT GCCTCCTGGA CTGTTCACGG CAGACCAGAA 2264 CGTTTCTGGC CTGGGTTTTG TGGTCATCTA TTCTAGCAGG GAACACTAAA 3314

TABLE 2 pAB-Back: 5′                               3′ ACC AGA AGC TTA TGA ATA TGC AAA TC′ Linker-Anti: 5′ GCC ACC CGA CCC ACC ACC GCC CGA TCC ACC GCC TCC                             3′ TGA GGA GAC GGT GAC CGT GGT C

TABLE 3 Linker-Sense: 5′ GGT GGA TCG GGC GGT GGT GGG TCG GGT GGC GGC GGA                               3′ TCT GAC ATC CAG CTG ACC CAG AGC VL(Mut)-For: 5′ TGC AGG ATC CAA CTG AGG AAG CAA AGT TTA AAT TCT                  3′ ACT CAC CTT TGA TC

TABLE 4 Pharmacokinetics of sFv-hu β Gluc fusion protein in CD1 nu/nu mice carrying MzStol ng of sFv-huβGluc per gram of tissue or ml of plasma measured in the triple determinant test Mouse Mouse Mouse Mouse Mouse Mouse Tissue 1 2 3 4 5a 5b type 0.05 h 3 h 24 h 48 h 120 h 120 h Tumor 24.8 4 7.7 2.1 2.2 6.2 Spleen 15.4 4.1 <0.1 <0.1 <0.1 <0.1 Liver 40.9 10.1 0.8 0.8 0.3 <0.1 Intestine 5.2 4.4 1.1 1.2 0.6 <0.1 Kidney 44.4 7 <0.1 <0.1 <0.1 <0.1 Lung 154.8 17.3 <0.1 <0.1 <0.1 <0.1 Heart 148.3 8.2 <0.1 <0.1 <0.1 <0.1 Plasma 630.9 95 2.7 0.4 <0.1 <0.1 i.v. injection of 0.8 μg of purified fusion protein per mouse

TABLE 5 Analysis of the monosaccharide components in the carbohydrate content of the sFv-huβ-Gluc fusion protein from BHK cells The purified sFv-huβ-Gluc fusion protein was investigated for its carbohydrate content. This revealed after hydrolysis the following individual components in the stated molar ratio (mol of carbohydrate/mol of sFv-huβ-Gluc). N-Acetyl N-Acetyl- Fucose Galactosamine glucosamine Galactose Glucose Mannose neuraminic acid sFv-huβ-Gluc 4 2 30 8 1 43 4

TABLE 6 Analysis of the monosaccharide components in the carbohydrate content of the sFv-huβGluc fusion protein from Saccharomyces cerevisiae. Glucosamine Glucose Mannose sFv-huβGluc 6 12 150 mol/mol (mol/mol)

TABLE 7 Oligos for sFv 431/26 cloning in pUC 19 sFv for (2561) 5′TTT TTA AGC TTA GAT CTC CAC CTT GGT C 3′ sFv back (2577) 5′AAA AAT CTA GAA TGC AGG TCC AAC TGC AGG AGA G 3′

TABLE 8 Oligos for hum.β-Gluc cloning in sFv pUC 19 Hum.β-Gluc. back oligo (2562) 5′AAA AAA GTG ATC AAA GCG TCT GGC GGG CCA CAG GGC GGG ATC CTG TAC 3′ Bum.β-Gluc for oligo (2540) 5′TTT TAA GCT TCA AGT AAA CGG GCT GTT 3′

TABLE 9 Oligos for sFv/hum-β-Gluc cloning in pIXY120 PCR oligo VHpIXY back (2587) 5′TTT TGG TAC CTT TGG ATA AAA GAC AGG TCC AAC TGC AGG AGA G 3′ PCR oligo VKpIXY for (2627) 5′A AAA CCA TGG GAA TTC AAG CTT CGA GCT GGT ACT ACA GGT 3′

TABLE 10 Oligos for E. coli β-Gluc cloning in sFv pUC 19 E. coli β-Gluc. for (2639) 5′TTT TAA GCT TCC ATG GCG GCC GCT CAT TGT TTG CCT CCC TGC TG 3′ E. coli β-Gluc. back (2638) 5′AAA AAG ATC TCC GCG TCT GGC GGG CCA CAG TTA CGT GTA GAA ACC CCA 3′

TABLE 11 Oligos for sFv/β-lactamase cloning in pIXY120 PCR oligo VHpIXY back (2587) 5′TTT TGG TAC CTT TGG ATA AAA GAC AGG TCC AAC TGC AGG AGA G 3′ PCR oligo VKpIXY/β-lactamase for (2669) 5′AAA AAG CTT AGA TCT CCA GCT TGG TCC C 3′ PCR oligo link/β-lactamase back (2673) 5′AAA GAA TTC TGA TCA AAT CCT CGA GCT CAG GTT CAC AAA AGG TAG AGA AAA CAG T 3′ linker PCR oligo β-lactamase for (2674) 5′TTT AAG CTT ATT TTA ATA AAT CCA ATG T 3′ 

1-26. (canceled)
 27. A nucleic acid sequence coding for a compound comprising two or more antigen binding regions linked to at least one prodrug-activating enzyme, wherein a) the antigen binding region consists of a single polypeptide chain; b) the single polypeptide chain is comprised of a first variable domain, a second variable domain and a polypeptide linker connecting the first variable domain and the second variable domain, wherein the nucleotide sequence encoding the polypeptide linker is formed by two partially overlapping PCR primers during a PCR reaction that links the first variable domain and the second variable domain; and wherein c) said compound has a bivalent or a multivalent structure and is glycosylated.
 28. The nucleic acid sequence of claim 27 wherein at least one antigen binding region comprises a variable domain of a heavy antibody chain and a variable domain of a light antibody chain (sFv fragment).
 29. The nucleic acid sequence of claim 27 wherein at least one of the antigen binding regions binds to a tumor-associated antigen (TAA).
 30. The nucleic acid sequence of claim 29, wherein said TAA is selected from the group consisting of an N-CAM, PEM, EGF-R, Sialyl-Le^(a), Sialyl-Le^(x), TFβ, GICA, GD₃, GD₂, TAG72, CA125, the 24-25 kDa glycoprotein defined by MAb L6 and CEA.
 31. The nucleic acid sequence of claim 27, wherein said prodrug-activating enzyme is selected from the group consisting of a lactmase, pyroglutamate aminopeptidase, D-aminopeptidase, oxidase, peroxidase, phosphatase, hydroxynitrile lysase, protease, esterase, carboxypeptidase and glycosidase.
 32. The nucleic acid sequence of claim 31, wherein the enzyme is a β-glucuronidase, which is selected from the group consisting of an E. coli β-glucuronidase, a Kobayasia nipponica β-glucuronidase, a Secale cereale β-glucuronidase and a human β-glucuronidase.
 33. The nucleic acid sequence of claim 27, wherein at least one of the antigen binding regions is linked to the enzyme via a peptide linker.
 34. The nucleic acid sequence of claim 27 coding for a humanized sFv fragment against CEA and a human β-glucuronidase.
 35. The nucleic acid sequence of claim 34, wherein said sequence is SEQ ID NO:
 1. 36. The nucleic acid sequence of claim 27 encoding SEQ ID NO:2.
 37. A vector containing the nucleic acid sequence of claim
 27. 38. A host cell containing the vector of claim
 37. 39. The host cell of claim 38, wherein said host cell is BHK, CHO, COS, Hela, insect, tobacco plant, yeast or E. coli cell.
 40. A transgenic mammal that is not human containing a nucleic acid sequence as claimed in claim
 27. 41. A process for preparing a compound which comprises a) introducing a nucleic acid sequence as claimed in claim 27 into an expression vector, b) introducing the expression vector into a host cell, c) cultivating the host cell, and d) isolating said compound. 